The proposed Coordinating Center will participate with the selected Clinical Centers and the National Heart, Lung and Blood Institute (NHLBI) in the design and performance of a randomized clinical trail to determine the best clinically useful techniques to prevent or minimize alloimmunization as a cause of refractoriness to platelet transfusion. One or more treatment arms will be compared with a control arm of routinely prepared random-donor platelet concentrates and routinely prepared red cell products. The coordinating Center will provide data management, reporting services, data analysis, and overall study coordination and management, and coordinate the function of the Central Laboratory as decided by the investigators. The Coordinating Center will design the study forms, write the protocol and manual of operations, and plan and implement randomization and study quality control procedures. Monthly quality control reports will be sent to the Clinical Centers and the NHLBI. Detailed reports on the accumulating data and Clinical Center performance will be provided every six months to the Data and Safety Monitoring Board (DSMB). Other analyses as required by the DSMB and the NHLBI will also be provided. The Coordinating Center investigators will function as executive secretariat and collaborate with other investigators in analyzing the study data for presentation and publication.